This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Although core histones are among the most conserved proteins in the cell, they bear an extensive population of methylations, acetylations, phosphorylations, and ubiquitination as well as particular additional key modifications throughout their sequences. The various combinations of different numbers of PTMs at different residue locations allow the cell to generate many different PTM configurations as well as alter particular sites dynamically in response to cellular cues. It has been proposed that those configurations are associated with epigenetic regulations. However, detailed characterization of core histones and their PTM configurations is thus far a difficult task. The difficulty for analysis of heavily modified histones arises from the fact that many, sometimes thousands of possible PTM configurations may exist due to the combinatorial nature of PTMs, occupying different sites. In this project, we intend to develop novel technologies to solve some of the most challenging problems in the mass spectrometry based proteomics filed.